<?php

/**
 * Lop nay duoc tham khao tu lop security trong CodeIgniter
 * 
 * */
class Core_Security
{

    protected $_xss_hash = '';
    /* never allowed, string replacement */
    protected $_never_allowed_str = array('document.cookie' => '[removed]',
        'document.write' => '[removed]', '.parentNode' => '[removed]', '.innerHTML' =>
        '[removed]', 'window.location' => '[removed]', '-moz-binding' => '[removed]',
        '<!--' => '&lt;!--', '-->' => '--&gt;', '<![CDATA[' => '&lt;![CDATA[');

    /* never allowed, regex replacement */
    protected $_never_allowed_regex = array("javascript\s*:" => '[removed]',
        "expression\s*(\(|&\#40;)" => '[removed]', // CSS and IE
        "vbscript\s*:" => '[removed]', // IE, surprise!
        "Redirect\s+302" => '[removed]');

    // --------------------------------------------------------------------

    /**
     * XSS Clean
     *
     * Sanitizes data so that Cross Site Scripting Hacks can be
     * prevented.  This function does a fair amount of work but
     * it is extremely thorough, designed to prevent even the
     * most obscure XSS attempts.  Nothing is ever 100% foolproof,
     * of course, but I haven't been able to get anything passed
     * the filter.
     *
     * Note: This function should only be used to deal with data
     * upon submission.  It's not something that should
     * be used for general runtime processing.
     *
     * This function was based in part on some code and ideas I
     * got from Bitflux: http://channel.bitflux.ch/wiki/XSS_Prevention
     *
     * To help develop this script I used this great list of
     * vulnerabilities along with a few other hacks I've
     * harvested from examining vulnerabilities in other programs:
     * http://ha.ckers.org/xss.html
     *
     * @param	mixed	string or array
     * @return	string
     */
    public function xss_clean($str, $is_image = false)
    {
        /*
        * Is the string an array?
        *
        */
        if (is_array($str))
        {
            while (list($key) = each($str))
            {
                $str[$key] = $this->xss_clean($str[$key]);
            }

            return $str;
        }

        /*
        * Remove Invisible Characters
        */
        $str = $this->remove_invisible_characters($str);

        // Validate Entities in URLs
        $str = $this->_validate_entities($str);

        /*
        * URL Decode
        *
        * Just in case stuff like this is submitted:
        *
        * <a href="http://%77%77%77%2E%67%6F%6F%67%6C%65%2E%63%6F%6D">Google</a>
        *
        * Note: Use rawurldecode() so it does not remove plus signs
        *
        */
        $str = rawurldecode($str);

        /*
        * Convert character entities to ASCII
        *
        * This permits our tests below to work reliably.
        * We only convert entities that are within tags since
        * these are the ones that will pose security problems.
        *
        */

        $str = preg_replace_callback("/[a-z]+=([\'\"]).*?\\1/si", array($this,
            '_convert_attribute'), $str);

        $str = preg_replace_callback("/<\w+.*?(?=>|<|$)/si", array($this,
            '_decode_entity'), $str);

        /*
        * Remove Invisible Characters Again!
        */
        $str = $this->remove_invisible_characters($str);

        /*
        * Convert all tabs to spaces
        *
        * This prevents strings like this: ja	vascript
        * NOTE: we deal with spaces between characters later.
        * NOTE: preg_replace was found to be amazingly slow here on 
        * large blocks of data, so we use str_replace.
        */

        if (strpos($str, "\t") !== false)
        {
            $str = str_replace("\t", ' ', $str);
        }

        /*
        * Capture converted string for later comparison
        */
        $converted_string = $str;

        // Remove Strings that are never allowed
        $str = $this->_do_never_allowed($str);

        /*
        * Makes PHP tags safe
        *
        * Note: XML tags are inadvertently replaced too:
        *
        * <?xml
        *
        * But it doesn't seem to pose a problem.
        */
        if ($is_image === true)
        {
            // Images have a tendency to have the PHP short opening and
            // closing tags every so often so we skip those and only
            // do the long opening tags.
            $str = preg_replace('/<\?(php)/i', "&lt;?\\1", $str);
        } else
        {
            $str = str_replace(array('<?', '?' . '>'), array('&lt;?', '?&gt;'), $str);
        }

        /*
        * Compact any exploded words
        *
        * This corrects words like:  j a v a s c r i p t
        * These words are compacted back to their correct state.
        */
        $words = array('javascript', 'expression', 'vbscript', 'script', 'applet',
            'alert', 'document', 'write', 'cookie', 'window');

        foreach ($words as $word)
        {
            $temp = '';

            for ($i = 0, $wordlen = strlen($word); $i < $wordlen; $i++)
            {
                $temp .= substr($word, $i, 1) . "\s*";
            }

            // We only want to do this when it is followed by a non-word character
            // That way valid stuff like "dealer to" does not become "dealerto"
            $str = preg_replace_callback('#(' . substr($temp, 0, -3) . ')(\W)#is', array($this,
                '_compact_exploded_words'), $str);
        }

        /*
        * Remove disallowed Javascript in links or img tags
        * We used to do some version comparisons and use of stripos for PHP5, 
        * but it is dog slow compared to these simplified non-capturing 
        * preg_match(), especially if the pattern exists in the string
        */
        do
        {
            $original = $str;

            if (preg_match("/<a/i", $str))
            {
                $str = preg_replace_callback("#<a\s+([^>]*?)(>|$)#si", array($this,
                    '_js_link_removal'), $str);
            }

            if (preg_match("/<img/i", $str))
            {
                $str = preg_replace_callback("#<img\s+([^>]*?)(\s?/?>|$)#si", array($this,
                    '_js_img_removal'), $str);
            }

            if (preg_match("/script/i", $str) or preg_match("/xss/i", $str))
            {
                $str = preg_replace("#<(/*)(script|xss)(.*?)\>#si", '[removed]', $str);
            }
        } while ($original != $str);

        unset($original);

        // Remove evil attributes such as style, onclick and xmlns
        $str = $this->_remove_evil_attributes($str, $is_image);

        /*
        * Sanitize naughty HTML elements
        *
        * If a tag containing any of the words in the list
        * below is found, the tag gets converted to entities.
        *
        * So this: <blink>
        * Becomes: &lt;blink&gt;
        */
        $naughty = 'alert|applet|audio|basefont|base|behavior|bgsound|blink|body|embed|expression|form|frameset|frame|head|html|ilayer|iframe|input|isindex|layer|link|meta|object|plaintext|style|script|textarea|title|video|xml|xss';
        $str = preg_replace_callback('#<(/*\s*)(' . $naughty . ')([^><]*)([><]*)#is',
            array($this, '_sanitize_naughty_html'), $str);

        /*
        * Sanitize naughty scripting elements
        *
        * Similar to above, only instead of looking for
        * tags it looks for PHP and JavaScript commands
        * that are disallowed.  Rather than removing the
        * code, it simply converts the parenthesis to entities
        * rendering the code un-executable.
        *
        * For example:	eval('some code')
        * Becomes:		eval&#40;'some code'&#41;
        */
        $str = preg_replace('#(alert|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si',
            "\\1\\2&#40;\\3&#41;", $str);


        // Final clean up
        // This adds a bit of extra precaution in case
        // something got through the above filters
        $str = $this->_do_never_allowed($str);

        /*
        * Images are Handled in a Special Way
        * - Essentially, we want to know that after all of the character 
        * conversion is done whether any unwanted, likely XSS, code was found.  
        * If not, we return TRUE, as the image is clean.
        * However, if the string post-conversion does not matched the 
        * string post-removal of XSS, then it fails, as there was unwanted XSS 
        * code found and removed/changed during processing.
        */

        if ($is_image === true)
        {
            return ($str == $converted_string) ? true : false;
        }

        return $str;
    }

    // --------------------------------------------------------------------

    /**
     * Random Hash for protecting URLs
     *
     * @return	string
     */
    public function xss_hash()
    {
        if ($this->_xss_hash == '')
        {
            if (phpversion() >= 4.2)
            {
                mt_srand();
            } else
            {
                mt_srand(hexdec(substr(md5(microtime()), -8)) & 0x7fffffff);
            }

            $this->_xss_hash = md5(time() + mt_rand(0, 1999999999));
        }

        return $this->_xss_hash;
    }

    // --------------------------------------------------------------------

    /**
     * HTML Entities Decode
     *
     * This function is a replacement for html_entity_decode()
     *
     * In some versions of PHP the native function does not work
     * when UTF-8 is the specified character set, so this gives us
     * a work-around.  More info here:
     * http://bugs.php.net/bug.php?id=25670
     *
     * NOTE: html_entity_decode() has a bug in some PHP versions when UTF-8 is the
     * character set, and the PHP developers said they were not back porting the
     * fix to versions other than PHP 5.x.
     *
     * @param	string
     * @param	string
     * @return	string
     */
    public function entity_decode($str, $charset = 'UTF-8')
    {
        if (stristr($str, '&') === false)
            return $str;

        // The reason we are not using html_entity_decode() by itself is because
        // while it is not technically correct to leave out the semicolon
        // at the end of an entity most browsers will still interpret the entity
        // correctly.  html_entity_decode() does not convert entities without
        // semicolons, so we are left with our own little solution here. Bummer.

        if (function_exists('html_entity_decode') && (strtolower($charset) != 'utf-8'))
        {
            $str = html_entity_decode($str, ENT_COMPAT, $charset);
            $str = preg_replace('~&#x(0*[0-9a-f]{2,5})~ei', 'chr(hexdec("\\1"))', $str);
            return preg_replace('~&#([0-9]{2,4})~e', 'chr(\\1)', $str);
        }

        // Numeric Entities
        $str = preg_replace('~&#x(0*[0-9a-f]{2,5});{0,1}~ei', 'chr(hexdec("\\1"))', $str);
        $str = preg_replace('~&#([0-9]{2,4});{0,1}~e', 'chr(\\1)', $str);

        // Literal Entities - Slightly slow so we do another check
        if (stristr($str, '&') === false)
        {
            $str = strtr($str, array_flip(get_html_translation_table(HTML_ENTITIES)));
        }

        return $str;
    }

    // --------------------------------------------------------------------

    /**
     * Filename Security
     *
     * @param	string
     * @return	string
     */
    public function sanitize_filename($str, $relative_path = false)
    {
        $bad = array("../", "<!--", "-->", "<", ">", "'", '"', '&', '$', '#', '{', '}',
            '[', ']', '=', ';', '?', "%20", "%22", "%3c", // <
            "%253c", // <
            "%3e", // >
            "%0e", // >
            "%28", // (
            "%29", // )
            "%2528", // (
            "%26", // &
            "%24", // $
            "%3f", // ?
            "%3b", // ;
            "%3d" // =
            );

        if (!$relative_path)
        {
            $bad[] = './';
            $bad[] = '/';
        }

        $str = $this->remove_invisible_characters($str, false);
        return stripslashes(str_replace($bad, '', $str));
    }

    // ----------------------------------------------------------------

    /**
     * Compact Exploded Words
     *
     * Callback function for xss_clean() to remove whitespace from
     * things like j a v a s c r i p t
     *
     * @param	type
     * @return	type
     */
    protected function _compact_exploded_words($matches)
    {
        return preg_replace('/\s+/s', '', $matches[1]) . $matches[2];
    }

    // --------------------------------------------------------------------

    /*
    * Remove Evil HTML Attributes (like evenhandlers and style)
    *
    * It removes the evil attribute and either:
    * 	- Everything up until a space
    *		For example, everything between the pipes:
    *		<a |style=document.write('hello');alert('world');| class=link>
    * 	- Everything inside the quotes 
    *		For example, everything between the pipes:
    *		<a |style="document.write('hello'); alert('world');"| class="link">
    *
    * @param string $str The string to check
    * @param boolean $is_image TRUE if this is an image
    * @return string The string with the evil attributes removed
    */
    protected function _remove_evil_attributes($str, $is_image)
    {
        // All javascript event handlers (e.g. onload, onclick, onmouseover), style, and xmlns
        $evil_attributes = array('on\w*', 'style', 'xmlns');

        if ($is_image === true)
        {
            /*
            * Adobe Photoshop puts XML metadata into JFIF images, 
            * including namespacing, so we have to allow this for images.
            */
            unset($evil_attributes[array_search('xmlns', $evil_attributes)]);
        }

        do
        {
            $str = preg_replace("#<(/?[^><]+?)([^A-Za-z\-])(" . implode('|', $evil_attributes) .
                ")(\s*=\s*)([\"][^>]*?[\"]|[\'][^>]*?[\']|[^>]*?)([\s><])([><]*)#i", "<$1$6", $str,
                -1, $count);
        } while ($count);

        return $str;
    }

    // --------------------------------------------------------------------

    /**
     * Sanitize Naughty HTML
     *
     * Callback function for xss_clean() to remove naughty HTML elements
     *
     * @param	array
     * @return	string
     */
    protected function _sanitize_naughty_html($matches)
    {
        // encode opening brace
        $str = '&lt;' . $matches[1] . $matches[2] . $matches[3];

        // encode captured opening or closing brace to prevent recursive vectors
        $str .= str_replace(array('>', '<'), array('&gt;', '&lt;'), $matches[4]);

        return $str;
    }

    // --------------------------------------------------------------------

    /**
     * JS Link Removal
     *
     * Callback function for xss_clean() to sanitize links
     * This limits the PCRE backtracks, making it more performance friendly
     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
     * PHP 5.2+ on link-heavy strings
     *
     * @param	array
     * @return	string
     */
    protected function _js_link_removal($match)
    {
        $attributes = $this->_filter_attributes(str_replace(array('<', '>'), '', $match[1]));

        return str_replace($match[1], preg_replace("#href=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si",
            "", $attributes), $match[0]);
    }

    // --------------------------------------------------------------------

    /**
     * JS Image Removal
     *
     * Callback function for xss_clean() to sanitize image tags
     * This limits the PCRE backtracks, making it more performance friendly
     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
     * PHP 5.2+ on image tag heavy strings
     *
     * @param	array
     * @return	string
     */
    protected function _js_img_removal($match)
    {
        $attributes = $this->_filter_attributes(str_replace(array('<', '>'), '', $match[1]));

        return str_replace($match[1], preg_replace("#src=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si",
            "", $attributes), $match[0]);
    }

    // --------------------------------------------------------------------

    /**
     * Attribute Conversion
     *
     * Used as a callback for XSS Clean
     *
     * @param	array
     * @return	string
     */
    protected function _convert_attribute($match)
    {
        return str_replace(array('>', '<', '\\'), array('&gt;', '&lt;', '\\\\'), $match[0]);
    }

    // --------------------------------------------------------------------

    /**
     * Filter Attributes
     *
     * Filters tag attributes for consistency and safety
     *
     * @param	string
     * @return	string
     */
    protected function _filter_attributes($str)
    {
        $out = '';

        if (preg_match_all('#\s*[a-z\-]+\s*=\s*(\042|\047)([^\\1]*?)\\1#is', $str, $matches))
        {
            foreach ($matches[0] as $match)
            {
                $out .= preg_replace("#/\*.*?\*/#s", '', $match);
            }
        }

        return $out;
    }

    // --------------------------------------------------------------------

    /**
     * HTML Entity Decode Callback
     *
     * Used as a callback for XSS Clean
     *
     * @param	array
     * @return	string
     */
    protected function _decode_entity($match)
    {
        return $this->entity_decode($match[0], strtoupper('utf-8'));
    }

    // --------------------------------------------------------------------

    /**
     * Validate URL entities
     *
     * Called by xss_clean()
     *
     * @param 	string	
     * @return 	string
     */
    protected function _validate_entities($str)
    {
        /*
        * Protect GET variables in URLs
        */

        // 901119URL5918AMP18930PROTECT8198

        $str = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-]+)|i', $this->xss_hash() .
            "\\1=\\2", $str);

        /*
        * Validate standard character entities
        *
        * Add a semicolon if missing.  We do this to enable
        * the conversion of entities to ASCII later.
        *
        */
        $str = preg_replace('#(&\#?[0-9a-z]{2,})([\x00-\x20])*;?#i', "\\1;\\2", $str);

        /*
        * Validate UTF16 two byte encoding (x00)
        *
        * Just as above, adds a semicolon if missing.
        *
        */
        $str = preg_replace('#(&\#x?)([0-9A-F]+);?#i', "\\1\\2;", $str);

        /*
        * Un-Protect GET variables in URLs
        */
        $str = str_replace($this->xss_hash(), '&', $str);

        return $str;
    }

    // ----------------------------------------------------------------------

    /**
     * Do Never Allowed
     *
     * A utility function for xss_clean()
     *
     * @param 	string
     * @return 	string
     */
    protected function _do_never_allowed($str)
    {
        foreach ($this->_never_allowed_str as $key => $val)
        {
            $str = str_replace($key, $val, $str);
        }

        foreach ($this->_never_allowed_regex as $key => $val)
        {
            $str = preg_replace("#" . $key . "#i", $val, $str);
        }

        return $str;
    }


    // --------------------------------------------------------------------

    /**
     * Remove Invisible Characters
     *
     * This prevents sandwiching null characters
     * between ascii characters, like Java\0script.
     *
     * @access	public
     * @param	string
     * @return	string
     */
    public function remove_invisible_characters($str, $url_encoded = true)
    {
        $non_displayables = array();

        // every control character except newline (dec 10)
        // carriage return (dec 13), and horizontal tab (dec 09)

        if ($url_encoded)
        {
            $non_displayables[] = '/%0[0-8bcef]/'; // url encoded 00-08, 11, 12, 14, 15
            $non_displayables[] = '/%1[0-9a-f]/'; // url encoded 16-31
        }

        $non_displayables[] = '/[\x00-\x08\x0B\x0C\x0E-\x1F\x7F]+/S'; // 00-08, 11, 12, 14-31, 127

        do
        {
            $str = preg_replace($non_displayables, '', $str, -1, $count);
        } while ($count);

        return $str;
    }

}
